The present invention relates to a temperature compensated pneumatic counterbalance stay, and more particularly to a stay which balances with a weight of a vertically pivotally operated closure unit such as a hatchback and hood of an automobile.
A counterbalance stay known as a gas spring is provided in an automobile for supporting a hatchback. The stay is extended when the hatchback is opened, and to the contrary, retracted when closed. Since the automobile is subjected to a wide range of ambient temperature, the pressure of the gas within a cylinder of the stay considerably varies. For example, in severe cold, the pressure of the gas is so reduced that the supporting force of the stay cannot hold the hatchback in the raised position. The disadvantage can be removed by increasing the initial pressure of the gas at charging. However, the gas pressure excessively rises under high temperature in summer, so that the hatchback cannot be lowered from the raised position without a large manual force. Consequently, it is desired that an improved counterbalance stay which is free of the disadvantage is provided.
U.S. Pat. No. 4,408,751 discloses a temperature compensated pneumatic counterbalance where a thermally actuated bimetallic disc valve is provided to compensate the change of pressure therein due to temperature variation. However, the bimetal has a small actuating force, and in addition, a low sensitivity.
An object of the present invention is to provide a pneumatic counterbalance stay wherein the pressure of gas in an expansible actuating chamber is decreased when the ambient temperature is increased, so that the closing unit held open can be easily closed.
According to the present invention, there is provided a pneumatic counterbalance stay comprising a cylinder charged with gas, a partitioning body fixed to an inner wall of the cylinder to separate the cylinder into an actuating chamber and a pressure accumulating chamber, a thermo-actuator provided in the partitioning body, the thermo-actuator having a heat conductive cylinder charged with wax pellets, a rubber seal bag secured to the conductive cylinder and provided in the wax pellets, and a rod axially slidably mounted in the cylinder and engaged with the seal bag and provided to be outwardly projected when ambient temperature is higher than a predetermined temperature, a plunger valve device provided in the partitioning body and comprising a plunger valve and a valve seat, the plunger valve being engaged with the rod of the thermo-actuator so as to be axially moved together with the rod and outwardly projected from the partitioning body, the valve seat being secured in the partitioning body adjacent the plunger valve, a piston rod connected to a piston slidably mounted in actuating chamber of the cylinder, an end of the piston rod being projected from the actuating chamber. The plunger valve is arranged to be engaged with the valve seat to close the plunger valve device when projected from the partitioning body by the thermo-actuator, and arranged to be disengaged from the valve seat to open the plunger valve device when retracted by a part of the piston.
In a feature of the present invention, the plunger valve has a large diameter portion and a small diameter portion, the valve seat is a cylindrical member around the plunger valve, the large diameter portion engages with the valve seat to close the plunger valve device.
These and other objects and features of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings.